This invention relates to an automatic ultrasonic fault detector, particularly useful to detect the faults or defects of welds of a welded pipe.
Nondestructive inspection of the welds of welded pipes has been generally carried out by the use of radioactive rays, ultrasonic wave or electric resistors. However, in a nuclear reactor of a nuclear power plant, when it is required to inspect the welds of the welded pipes, after starting the operation of the reactor, it has been desirable to adopt an ultrasonic fault detecting method because radioactive atmosphere is surrounding the portions to be inspected and the welded pipes are filled with water. Furthermore, the ultrasonic fault detection method is suitable for automatic remote operation for the reason that the detected informations can be remotely indicated.
Generally, in such ultrasonic fault detection methods, it is desired that the ultrasonic fault detector essentially comprises a probe for transmitting and receiving an ultrasonic wave, a probe head for holding the probe, and a contact medium (e.g. water or oil) effectively transmitting the ultrasonic wave to an object to be inspected. In field work, water is usually used only once as the contact medium and discharged at usual inspections, but the water used in a nuclear power plant becomes radioactive and it is expensive to process it to a nonradioactive state. It is therefore desirable to recirculate the radioactive water as the contact medium in the nuclear reactor.
In the prior art, although the ultrasonic fault detection of a large diameter welded pipe was carried out by moving the detector along guide rails, the situation might occur where the load applied on a driving motor will vary thereby periodically varying the gap between the surface of the pipe to be inspected and the probe during the fault detecting operation. Furthermore, ultrasonic fault detection of the welded pipe having a small diameter could not be effectively carried out by the prior art method because the detector is too large for the small pipe, and there has been no efficient ultraonic fault detector suitable for the reactor container of the nuclear power plant where a number of pipes of small diameters are densely arranged.